The present invention relates to communications methods, apparatus and computer program products, and more particularly, to channel characterization and symbol estimation methods, apparatus, and computer program products.
Wireless communications techniques are widely used to communicate information, such as voice information or data for applications, such as video or web page information. A variety of different radio interfaces may be used for such wireless communications, including those that use frequency division multiple access (FDMA) techniques, time division multiple access (TDMA) techniques, and code division multiple access (CDMA) techniques.
In a typical CDMA wireless system, channels for communicating between entities, e.g., between a cellular base station and a wireless terminal, such as a cellular telephone, are defined through the use of spreading codes that spread transmitted radio frequency signals across a shared spectrum. As is well known, signals encoded in such a fashion may be recovered at a receiving station through knowledge of the spreading code.
In CDMA systems, transmit power may be controlled to reduce interference between channels and, thus, maximize system capacity. For example, third generation CDMA system standards, including both Wideband-CDMA (WCDMA) and IS-2000, include provisions for fast and slow downlink power control mechanisms. With fast downlink power control, a terminal (e.g., mobile station) requests that the downlink power be either +x dB or −x dB for a future block of data. In WCDMA, the block of data is a slot, whereas in IS-2000, the block of data is referred to as a power control group. The value of x is typically 1 dB or less and is known at the mobile station.
The base station may respond to the power control request in many ways. It may receive the request correctly and perform the requested change. If the power has reached a maximum or minimum allowed per-user power level, the base station may ignore the request. If the request is received in error, the base station may incorrectly respond. The base station may also ignore the request entirely.
The base station may also adjust downlink power more slowly due to open-loop power control and transmit power limitations. Open-loop power control may be performed based on the received power at the base station.
Early versions of the W-CDMA standard proposed the use of dedicated pilot symbols in traffic channels for traffic channel estimation, providing a way to track traffic channel changes resulting from fast power control. However, a common pilot channel has been recently introduced in W-CDMA. The current IS-2000 standard includes a common pilot channel that is available for channel estimation, but does not include pilot symbols within the traffic channels.